This invention relates to a process for continuously producing in a high yield tert-butyl alcohol (abbreviated as "TBA" hereinunder) from isobutylenes and water by using a strongly acidic cation exchange resin as a catalyst. In particular, this invention is concerned with a process for continuously producing TBA in a high yield without the addition of a third substance such as reaction aiding agents.
It has been well known heretofore to produce TBA by hydrating isobutylenes with use of sulfuric acid having a variety of concentrations. Although the method produces TBA in a comparatively higher yield, it has such defects as producing an isobutylene polymer as a by-product, inability to maintain every part of the equipment safe for a long period due to the use of corrosive sulfuric acid and required treating of waste sulfuric acid.
A direct hydration method of isobutylenes employing phosphoric acid as a catalyst has also been known, however, it requires high temperature and pressure conditions, and the yield of TBA is low.
Further, as to the synthesis of TBA by direct hydration with use of a cation exchange resin catalyst, many methods have been proposed. For example, in Industrial and Engineering Chemistry, vol. 53, No. 3, pp. 209-211, a method in which isobutylene is continuously hydrated by using an ion exchange resin catalyst is disclosed, however, the rate of conversion of isobutylene is about 30% at the highest. In fact, water and isobutylene form a heterogeneous system, and it is difficult to attain an effective reaction between them by merely bringing isobutylene into contact with water in the presence of said catalyst. This fact is also clear from the description of specifications of Japanese Patent Laid-Open Publications Nos. 50-32116, 50-126603, 50-137906 and 51-59802, etc. In order to eliminate the defect, a number of other methods such as adding organic acids in the reaction system as a reaction aiding agent (Japanese Patent Laid-Open Publication Nos. 50-32116 and 50-126603), adding alcohols (Japanese Patent Laid-Open Publication No. 50-137906) and using polar solvents such as ethyl Cellosolve and dioxane and further using emulsifiers, if necessary (Japanese Patent Laid-Open Publication No. 51-59802), have been studied by a number of those skilled in the art heretofore. However, all these methods of add reaction aiding agents have many inconveniences including the addition of a third substance itself, and separating and recovering the reaction aiding agents and separating TBA from the water layer containing them.
Further, a method for hydrating isobutylene by using an ion exchange resin in the state of a suspension is known (Japanese Patent Publication No. 40-2408). The method comprises taking isobutylene, water and a catalyst in a reactor, mixing and stirring to form a suspension thereof, separating the reaction mixture from the reactor into a water layer and an oil layer and recycling of the water layer containing the catalyst in suspension to the reactor. On the one hand, the method may have an advantage in its own way, however, it has defects in that the stirring necessary for keeping the catalyst in a suspension inevitably produces wear and breakdown of the catalyst, and in that at the same time a troublesome operation in which a liquid including the suspended catalyst is treated by recycling is required. Accordingly, in fact, the method is difficult to be performed on an industrial scale.
In particular, when a strongly acidic cation exchange resin such as is employed in this invention is used as a catalyst, the wear and breakdown of the catalyst are further remarkable because the mechanical strength of the resin is weak due to a number of micro-porous structures or cells in the interior thereof. Further, when the catalyst according to this invention is employed in the method in which reaction aiding agents such as an organic acid, alcohol, ethyl Cellosolve, dioxane, surface active agent, etc. are added and reacted in the reaction system, the swelling and deformation of the resin frame resulting from the polar groups of the reaction aiding agent are remarkable, and catalyst life is largely restricted. Therefore, it is very difficult to perform commercially these methods with use of the strongly acidic cation exchange resin having a high catalytic activity of this invention.
As a result of hard studies of various methods for continuously producing TBA in order to remove the defects of the methods heretofore known, the inventors have found the fact that TBA is obtained very effectively by bringing water into contact with isobutylenes, which originally form non-homogeneous or heterogeneous mixtures with the former, by the prescribed method on the surfaces of the specific strongly acidic cation exchange resin catalyst particles and have completed this invention.